To manufacture a thin disc such as a semiconductor wafer, an elongated billet of semiconductor material is cut into very thin slices, about 1/2 mm in thickness. The slices or wafers of semiconductor material are then lapped and polished by a process that applies an abrasive slurry to the wafer's surfaces. After polishing, slurry residue conventionally is cleaned or scrubbed from wafer surfaces via a scrubbing device which employs polyvinyl acetate (PVA) brushes, brushes made from other porous or sponge-like material, or brushes made from nylon bristles or similar materials. Although these conventional cleaning devices remove a substantial portion of the slurry residue which adheres to wafer edges, slurry particles nonetheless remain and produce defects during subsequent processing.
A conventional PVA brush scrubber disclosed in U.S. Pat. No. 5,675,856 is shown in the side elevational view of FIG. 1. The conventional scrubber 11, shown in FIG. 1, comprises a pair of PVA brushes 13a, 13b. Each brush comprises a plurality of raised nodules 15 across the surface thereof, and a plurality of valleys 17 located among the nodules 15. The scrubber 11 also comprises a platform 19 for supporting a wafer W and a mechanism (not shown) for rotating the pair of PVA brushes 13a, 13b. The platform 19 comprises a plurality of spinning mechanisms 19a-c for spinning the wafer W.
Preferably, the pair of PVA brushes 13a, 13b are positioned to extend beyond the edge of the wafer W, so as to facilitate cleaning the wafer's edges thereof. However, research shows that slurry induced defects still occur, and are caused by slurry residue remaining along the edges of the wafer despite cleaning with apparatuses such as that described above. Specifically, subsequent processing has been found to redistribute slurry residue from the wafer edges to the front of the wafer, causing defects.
A number of devices have been developed to improve wafer edge cleaning. One such device is shown in the side elevational view of FIG. 2. This mechanism employs a separate edge brush 21, which is driven by a separate motor (not shown), that causes the edge brush 21 to rotate. The edge brush 21 fits over the edge of the wafer W as shown in FIG. 2, providing more effective wafer edge cleaning. Although the edge brush 21 addresses the need to clean slurry residue from wafer edges, it does so at the expense of increased scrubber complexity and cost, and requires additional solvents (e.g., water and ammonia) to maintain the cleanness of the edge brush 21 over an extended numbers of wafers.
Accordingly the field of wafer cleaning requires a method and apparatus which effectively cleans both the flat surfaces and the edge surfaces of a semiconductor wafer, and that does so without increased cost and complexity. In short, the semiconductor processing field needs an effective scrubber that satisfies the ever-present demand for reduced cost per unit wafer processed.